Dielectric energy storage technology has the advantages of high power density, fast charging and discharging speed, long service life, and good high temperature stability, so it has a wide range of application prospects in renewable energy, electric vehicles and other fields. Although dielectric energy storage technology has high power density, its energy storage density is far less than that of mainstream battery energy storage technology, so the research and development of high energy storage density dielectric materials has become a highly competitive research frontier in the field of energy materials.
Among dielectric materials, relaxed ferroelectrics have high dielectric energy storage performance due to their unique polar nanodomain structure, but the contradictory relationship between polarization strength and breakdown field strength that is common in dielectric materials still restricts further breakthroughs in their energy storage density. The research group of Professor Li Jingfeng from the School of Materials Science and Technology of Tsinghua University jointly proposed the introduction of the "polar sorbet blocking" strategy into the relaxed ferroelectric films, and the aerogel method was used to prepare the relaxed ferroelectric films with energy storage densities as high as 202 J/cm3. The research was published online in Science on July 12, 2024.
This strategy breaks through the energy storage density by achieving a highly localized strong polarity in the relaxed ferroelectric. Firstly, by constructing a chaotic slush nanodomain structure, the high reversible polarization intensity that is difficult to obtain in conventional relaxed ferroelectrics is realized. Then, a network structure constructed by grain boundaries and nano-amorphous phases was introduced to segment the slush nanodomain structure, and a new type of relaxed ferroelectric with an isolated polar-slush (IPS) structure was constructed (Fig. 1). The simulation and experimental results show that the IPS structure can synergistically improve the reversible polarization strength and breakdown field strength, and the high energy storage density, efficiency and performance can be obtained based on component optimization.
Fig.1 Phase field simulation of polar slush blockage strategy and its polarization and energy storage characteristics in relaxed ferroelectric
With the help of high-throughput phase field simulations, the research team carried out experimental designs in Bi(Mg0.5Ti0.5)O3-SrTiO3(BMT-ST)-based relaxation ferroelectric thin films. Through a large amount of Bi doping, strong covalent Bi-O bonds and unique defect structures are introduced, resulting in the formation of polar slush, followed by grain boundaries and amorphous caused by excess Ti, and the IPS structure is formed. The reversible polarization strength and breakdown field strength of the film reach ~77 μC/cm2 and ~7 MV/cm, respectively, and its energy storage density exceeds 200 J/cm3 with an energy storage efficiency of ~79% (Fig. 2). At the same time, the film exhibits excellent charge-discharge cycle reliability and stable performance over the temperature range of 25-225°C. The research team also fabricated large-area films on commercial 4-inch (10.16 cm diameter) silicon wafers, which showed excellent thickness uniformity and performance consistency, as well as higher energy storage performance than other reported large-size films.
Fig.2 Polarization, electrical and energy storage properties of different types of BMT-ST-based relaxation ferroelectric films
Using second-order nonlinear optical (SHG) scanning detection, nanobeam precession electron diffraction (PED), and high-resolution scanning transmission electron microscopy (STEM), the research team demonstrated the existence of highly localized strong polarity properties in IPS-structured films, which arise from the combined effect of embedded amorphous phases, high-density grain boundaries, subgrain boundaries composed of dislocation arrays, and polar slush clusters (Fig. 3). The structure combines high insulation with highly dynamic polar clusters, which significantly enhances the energy storage performance of the material.
Fig.3 Structural characterization of different types of BMT-ST-based relaxation ferroelectric films
The results were published in the internationally renowned journal Science under the title of "Partitioning polar-slush strategy in relaxors leads to large energy-storage capability". Shu Liang, a 2019 doctoral student in the School of Materials, Shi Xiaoming, a lecturer at the University of Science and Technology Beijing, Zhang Xin, a 2022 doctoral student in the School of Materials, and Yang Ziqi, a postdoctoral fellow in the School of Materials, are the co-first authors of the article, and Professor Li Jingfeng of Tsinghua University, Professor Zhang Shujun of the University of Wollongong in Australia and Professor Huang Houbing of Beijing Institute of Technology are the co-corresponding authors of the article. Important collaborators of the paper include Associate Professor Li Qian of the School of Materials Science and Technology of Tsinghua University. This work was supported by the National Natural Science Foundation of China (NSFC) and the Tsinghua University-Toyota Research Center Collaboration Project.
Paper Links:
https://www.science.org/doi/10.1126/science.adn8721